1. Technical Field
The present application relates to a cutting insert having a bearing surface and a rake face at a distance therefrom and at least one flank arranged at a positive clearance angle, said rake face and flank forming an encircling round or polygonal cutting edge, and having at least one cutting edge point at a maximum distance from a plane in which the bearing surface lies, and having at least one cutting edge point at a minimum distance from the same plane.
2. Background Information
Background information is for informational purposes only and does not necessarily admit that subsequently mentioned information and publications are prior art.
The cutting inserts described above include the “positive cutting inserts” which in plan view can be circular, essentially triangular, quadrilateral, possibly square, rhombic or rectangular. The cutting edge is formed by the adjoining rake face and one or more flanks. In the simplest case, the rake face is of planar design, i.e. the rake angle is zero degrees.
Some types of cutting inserts have a sloping side which adjoins the cutting edge on the rake face, thereby forming a positive rake angle. Some types of cutting edges have a wavelike design, adjoining which are rake face sections of wavelike design. Finally, cutting edge rounding or the arrangement of a bevel at a positive or negative angle may be utilized in order to essentially restrict or minimize chipping of a cutting edge.
To machine some surfaces, such as the running surfaces of railroad wheels, cutting inserts may be used which have a circular cutting edge of constant height and a constant positive clearance angle. The frustoconical cutting inserts are used for facing the running surfaces. After wear of the actively used cutting edge, the cutting inserts can be arranged such as to be shifted in the tool carrier by a rotation angle of ninety degrees or one hundred twenty degrees depending on the original cutting depth, after which a new unused cutting edge region can be utilized.
Indexable inserts of the type described, having a circular cutting edge of constant height, disadvantageously tend to vibrate, or “chatter,” during the machining operation. Due to these uncontrolled vibratory movements during the machining, irregularities (chatter marks) are produced on the surface of the machined workpiece. Apart from this poor surface quality of the machined workpiece, the service life of such indexable inserts proves to be relatively short.
Also known in principle are indexable inserts of the type mentioned at the beginning in which the cutting edge or one of the cutting edges has a maxima and cutting edges, in each case sloping therefrom on both sides, down to a cutting edge minimum. However, unlike in the case of negative cutting inserts having a clearance angle of zero degrees, lowering of the cutting edge in regions acts on the existing flank in such a way that the original cutting edge shape is changed.
Some tools have a toolholder having at least one recess for accommodating and for fastening a cutting insert of the type described above. Depending on the machining operation selected, effective rake angles can also be set via the arrangement of the cutting insert in the toolholder, which rake angles can be varied within limits in the axial and radial directions by tilting the cutting insert.